What is grey mould and how to fix it
Grey mould (Botrytis) is a common fungal disease that affects soft plant tissue, especially in cool, damp conditions. It shows up as a fuzzy grey coating and can spread quickly if ignored.
It looks worse than it is — but you do need to act early.
Quick answer: what is grey mould
Grey mould is a fungal disease that causes soft rot and a grey, fuzzy coating on leaves, stems, or flowers. Improve airflow, reduce moisture, and remove affected material to control it.
5 step guide to fixing grey mould
Step 1: Remove infected material
- Cut off affected leaves, stems, or flowers
- Dispose of them — don’t compost
- This slows the spread immediately
Step 2: Improve airflow
- Space plants out
- Open up dense growth
- Ventilate indoor areas or propagators
Step 3: Reduce moisture
- Avoid overwatering
- Water at soil level, not over leaves
- Let surfaces dry between watering
Step 4: Adjust environment
- Keep conditions cool but not damp
- Avoid high humidity with poor airflow
- Reduce condensation in enclosed spaces
Step 5: Treat if needed
- Use a fungicide if the problem persists
- Apply early rather than late
- Combine with better conditions
Best varieties & why (less prone plants)
- Zinnia
- More tolerant of dry air and good airflow
- Marigold
- Herbs like thyme and rosemary
Soft, lush plants and dense foliage are more at risk.
Common issues, pests & diseases
Grey fuzzy growth on leaves or stems
- Classic grey mould
- Often appears on damaged or dying tissue
Soft rot in stems or flowers
- Tissue breaks down quickly
- Remove immediately
Mould spreading across trays
Seedlings collapsing
Best fertiliser, soil, lighting & growing conditions
- Light
- Good light helps keep plants dry and healthy
- Soil
- Water
- Even watering, not excessive
- Feeding
- Avoid overfeeding (soft growth is more vulnerable)
Strong, balanced growth reduces risk.
Time of year
- Most common in cool, damp conditions
- Often seen in spring and autumn
- Common in greenhouses and indoor setups
Climate and regional notes
UK & Ireland
- High risk due to damp conditions
- Ventilation is critical
Europe
- Northern regions similar to UK
- Southern regions less affected unless humidity is high
USA
- More common in humid climates
- Indoor environments can create ideal conditions
Pro tips for prevention
- Always prioritise airflow
- Avoid overcrowding plants
- Remove dead or damaged material quickly
- Water early in the day
- Don’t let moisture sit on leaves
10 frequently asked questions about grey mould
What causes grey mould
Damp conditions, poor airflow, and plant stress.
What does grey mould look like
Grey, fuzzy coating on plant tissue.
Is grey mould dangerous
It can spread quickly, but is manageable.
Can plants recover from grey mould
Yes, if treated early.
Should I remove infected leaves
Yes, immediately.
Can I compost infected material
Best not to — it can spread spores.
Does watering affect grey mould
Yes, excess moisture increases risk.
Is grey mould the same as damping off
No, but both are fungal and related to moisture.
Do I need fungicide
Only if conditions alone don’t control it.
How do I prevent it coming back
Improve airflow and reduce moisture.
Related guides